The invention relates to a composition which is polymerizable by actinic radiation, in particular by light, and comprises
a) a constituent which can undergo free-radical polymerization, contains at least one terminal ethylenically unsaturated group and has a boiling point above 100.degree. C. under normal pressure, PA1 b) a compound which is capable of initiating the polymerization of constituent (a), under the action of actinic radiation, and PA1 c) a saturated copolymer as a binder, which is insoluble in water and soluble in aqueous-alkaline solutions. PA1 excessive tackiness of the resist layer, PA1 poor adhesion of the photopolymer layer to the polyester support film, PA1 insufficient adhesion to copper, PA1 brittleness in the exposed state, PA1 long development times, PA1 inadequate resistance in etching and electroplating processes, PA1 unsatisfactory toughness for tenting, PA1 poor stripping behavior. PA1 a) a constituent which can undergo free-radical polymerization, contains at least one terminal ethylenically unsaturated group and has a boiling point above 100.degree. C. under normal pressure, PA1 b) a compound which is capable of initiating the polymerization of constituent (a) under the action of actinic radiation, and PA1 c) a saturated copolymer which is insoluble in water and soluble in organic solvents and in aqueous-alkaline solutions, and which comprises units of
Photopolymerizable compositions of the indicated type are known and are used, inter alia, in the preparation of photopolymerizable printing plates and photoresist materials. An important field of application for such compositions is the preparation of dry photoresist materials.
DE-A 20 64 080 describes compositions of this type that contain, as binders, copolymers of methacrylic acid and alkyl methacrylates having at least four carbon atoms in the alkyl group, preferably terpolymers of methacrylic acid, methyl or ethyl methacrylate and an alkyl methacrylate having 4 to 15 carbon atoms in the alkyl group.
It is stated that an acid number in the range from 150 to 250 is necessary, in order to achieve developability in aqueous-alkaline media. In the case of layer thicknesses of at least 20 .mu.m, polymers having acid numbers above 200 are invariable employed. The developers used are generally particularly active and comprise, for example, aqueous solutions of sodium metasilicate and organic additions.
DE-A 23 63 806 describes similar compositions which, with a view to reducing cold flow in the unexposed state, contain terpolymers of methacrylic acid, an alkyl methacrylate and a further monomer, the homopolymer of which has a glass transition temperature of at least 80.degree. C. As monomers of this type, styrene, substituted styrenes and acrylonitrile are, in particular, mentioned. Also in this case, acid numbers of 170 to 250 are recommended.
Similar compositions based on the aboveindicated copolymers having an average molecular weight in the range from about 50,000 to 200,000 and acid numbers which are preferably in the range from 170 to 250 are described in DE-A 34 27 519.
In all binders having high acid numbers the desired easy developability is accompanied by reduced resistance of the light-hardened areas to alkaline solutions, for example, to the developer or to alkaline etching solutions.
DE-B 25 17 656 describes other compositions similar to those described above, which are intended for use in the preparation of dry resist materials and require, as a binder, a combination of two acidic polymers. Under certain conditions, one of these polymers is soluble in dilute aqueous sodium hydroxide solution and the other is insoluble. It is naturally technically more expensive to prepare a composition which must contain two binders of different solubilities and the composition is more prone to disintegration upon standing in solution or during the drying process than is a composition containing a uniform binder. There may also be a risk of constituents of the more difficultly soluble polymer separating from the solution in the developer and restricting the further use of the developer.
DE-A 30 28 136 describes similar photopolymerizable compositions which are suitable for the preparation of dry resists. The polymerizable compounds contained in these compositions comprise, inter alia, polyethylene glycol di(meth)acrylates. The binders used comprise copolymers of (meth)acrylic acid and alkyl(meth)acrylates, in particular terpolymers of methacrylic acid, methyl methacrylate and an alkyl(meth)acrylate having a relatively long alkyl group. The polymers used in the compositions have relatively high glass transition temperatures and thus impart a relatively high brittleness to the photocrosslinked composition. Brittleness is compensated for by a comparatively high monomer content, in particular by the above-mentioned strongly plasticizing monomers, but the high monomer content leads to a deterioration of other properties, such as resistance to aqueous, e.g. alkaline treating solutions, or cold flow.
DE-A 21 64 518 describes photopolymerizable compositions containing polymers with lateral (meth)acrylic ester groups. The compositions there described are processed into planographic printing plates having layer thicknesses of not more than 3 .mu.m. The saturated base polymers used for the preparation of the unsaturated polymers contain units of unsaturated carboxylic acids, (meth)acrylic esters, (meth)acrylonitrile, vinyl aromatic compounds and the like.
The suitability of photopolymerizable compositions for use in dry photoresist materials depends on the proper mutual coordination of various properties, for example, softness of the layer, adhesion to films, adhesion to copper, flexibility, developability, resistance to etching solutions and electroplating baths, applicability to the covering of drilled holes (tenting) and strippability. The known photopolymerizable compositions which can be processed in aqueous-alkaline solutions have one or more of the following disadvantages: